Claire Hadden was seven months pregnant when she woke up with a piercing pain in her stomach.

“I thought it was probably a stomach bug,” the 37-year-old mother of three told ABC News, recalling the Thanksgiving weekend scare. “I really did not feel well at all.”

Hadden went to the hospital the following day, but doctors found nothing out of the ordinary and sent her home. The next morning, she was overcome with shivers, so she went back to the hospital. Only this time, she made the trip an ambulance.

As a radiologist waved an ultrasound wand around her bulging belly, she told her to stop.

“It’s right here,” she said, referring to the upper right side of her abdomen. “Right here is whatever is causing the issue.”

The pain was coming from Hadden’s appendix, the small pouch that usually protrudes from the large intestine into the lower right corner of the abdomen. Only Hadden’s had moved – a lot.

It turns out a woman’s appendix can move up to eight inches during pregnancy, depending on her height and how far along she is, according to Dr. Alexander Greenstein, a surgeon at Mount Sinai Hospital in New York City.

“The more pregnant they are, the more the appendix gets pushed up and out of the way,” said Greenstein, who operated on Hadden. “When they get bigger and bigger and bigger like Claire was, it’s harder and harder to find.”

Using a tiny camera threaded laparoscopically through Hadden’s belly button, Greenstein was able to locate the appendix and remove it without disturbing the fetus.

Greenstein said the radiologist caught Hadden’s appendicitis just in time. Had the pouch ruptured and spilled its contents into her abdomen, she could have lost the baby. Hadden, too, could have died.

“I don’t think it sunk in until later,” Hadden said.

Greenstein said the pain of pregnancy can sometimes mask the signs of appendicitis. Similarly, pregnancy symptoms can sometimes be mistaken for appendicitis, according to research he conducted as a medical resident. Of 100 pregnant women who showed signed of appendicitis, only 30 of them actually had one, he said. It’s estimated that fewer than 0.15 percent of women have appendicitis during pregnancy.

Hadden said she felt better after delivering a healthy baby boy in February, but added that “ghost pain” lingered for several months.